Conventionally, a capillary thermal type mass flow rate sensor or a silicon-made ultra-small-sized thermal type mass flow rate sensor by making use of micro-machine technologies has been widely used to measure a mass flow rate of a liquid in the technical fields such as chemical analysis equipment and the like.
The former, or a capillary thermal type mass flow rate sensor is characterized by that the sensor allows its gas contacting faces to be made of stainless steel due to the structure, thus enabling to enhance the corrosion resistance to fluids to be measured at ease.
However, the capillary thermal type mass flow rate sensor is required to be equipped with a resistance wire for a heater to be wound to heat a capillary tube, thus causing a problem that may lead to unevenness in property among the products.
Another problem may be that the response speed of a mass flow rate sensor becomes slow due to the relatively large heat capacities of the capillary tube and the resistance wire for a heater.
On the other hand, along with the development in so-called micro-machine technologies in recent years, the development and utilization of the latter, or a silicon-made ultra-small-sized thermal type mass flow rate sensor has been widely under way. It has now become popular not only in the chemical-related fields but also in the industrial fields such as an automobile industry and the like due to the reason that a silicon-made ultra-small-sized thermal type mass flow rate sensor can be manufactured under a single processing, thus reducing the unevenness in property among the products, and achieving the extremely fast response speed as a sensor by making heat capacities small by downsizing, all of which are regarded as excellent characteristics of the sensor.
However, it is noted that there exist many problems to be solved with the said silicon-made ultra-small-sized thermal type mass flow rate sensor. Among other things, corrosion resistance is one that is needed to be solved urgently. That is, a silicon-made ultra-small-sized mass flow rate sensor employs silicon to form gas contacting faces. Therefore, a fundamental difficulty is that it can be easily corroded by fluids in a halogen family and the like.
Furthermore, organic materials such as an epoxy resin, an O-ring and the like are used as sealing materials for the mass flow rate sensor, thus making the emission of particles and the occurrence of the outside leak unavoidable. Accordingly, it becomes unable that the sensor is applied for the gas supply line and the like in semiconductor manufacturing facilities.
At the same time, various technologies have been developed so far to solve difficulties the afore-mentioned silicon-made ultra-small-sized thermal type mass flow rate sensor faces.
For example, with the TOKU-KAI No.2001-141540, the TOKU-KAI No.2001-141541, there is provided a heat resistance layer E6 on the outermost layer of a film E formed on the upper face of the frame D made from a silicon substrate A as shown in FIG. 18. With FIG. 18, E1˜E3 designate silicon oxide layers to form a film E, E4 a silicon nitride layer, E5 platinum, and C a lead connecting hardware.
[Patent Literature 1]
TOKU-KAI No. 2001-141540 Public Bulletin
[Patent Literature 2]
TOKU-KAI No. 2001-141541 Public Bulletin